Electric switches



Dec. 18, 1962 G. L. WHIFFIN 3,069,516

ELECTRIC SWITCHES Filed March 16, 1960 8 m V 3 I 2 /3a /4 F4 INVENTOFP GEOFPGE LESLIE W FF/N HTTOFPNEY United States Patent 3,069,516 ELECTRIC SWITCHES George Leslie Whiiiin, Harlow, England, assignor to Associated Electrical Industries Limited, London, England, a company of Great Britain Filed Mar. 16, 1960, Ser. No. 15,443 Claims priority, application Great Britain Apr. 3, 1959 8 Claims. (Cl. 2.0067) This invention relates to electric switches and more particularly to snap action switches as are used for control and regulating purposes. The switching gap between the movable and fixed contacts of such switches is usually very small, of the order of one hundredth of an inch for instance, and for ensuring similar operating characteristics for a great number of switches of a series, it is desirable that the switching gap be accurately adjusted, and

ecurely maintained during the life of the switch. l The present invention aims at providing an improved construction which fulfils these requirements yet is sim ple, time saving and well suited for assembly by machinery which may be automatic.

Another advantage offered by the invention is that if desired a contact surface which is set for operation may be removed for widening the gap between it and the stationary contact surface to allow servicing and cleaning of the co-operating contact surfaces, and may be accurately reset.

Generally this invention resides in an electric switch having a movable contact and a co-operating stationary contact, wherein the end position of one of the contacts defining a switching gap between the contacts is determined by a member frictionally engaging with its outer surface the surface of a recess in a fixed support for the said member, the frictional force being selected to allow sliding displacement between said member and support by a force parallel to the contact pressure but exceeding the said pressure.

The friction member may be deformable so as to increase its transverse dimension, thereby increasing the pressure between its outer surface and the surface of the recess, and the friction between these surfaces, when force is exerted in the longitudinal direction of the member which is parallel to the direction of contact movement and contact pressure. To this end the friction member may be provided with one or more slits extending in the longitudinal direction of the member and across the transverse dimension of the member.

With a construction according to the invention the adjustment of the switching gap can be carried out readily, using automatic machinery if desired. The stationary and movable contacts are assembled with a feeler gauge inserted between them, and pressure is exerted against the end of the friction member remote from the contacts while the stationary contact is held securely in position. Then the friction member slides in its support until the movable contact bears through the intermediary of the feeler gauge against the stationary contact. When movement in the direction of the force is thus stopped the friction member is further compressed and it may be adapted to expand now in its transverse direction under the compression force, thereby to intensify the friction. Finally the compressing force is removed and the feeler gauge is withdrawn from the gap.

More details will be apparent from the following description referring to the single FIGURE of the accompanying drawing which shows diagrammatically and by Way of example an embodiment of the invention, preferred at present, in which the friction member forms a stop or rest against which a movable contact bears when not engaging a stationary contact which co-operates with it. However, it will be understood that the invention also 3,069,516 Patented Dec. 18, 1962 ice embraces embodiments in which the stationary contact of a contact arrangement is carried by the friction member. Thus either a stop for a movable contact, or a carrier for a stationary contact, or both, can be made adjustable to allow adjustment of the switch gap, and the invention is applicable not only to simple make-andbreak switches, but also to change-over switches where a movable contact co-operates with a front contact and a back contact.

Referring now to the drawing,a switch frame 13 is rigidly connected, such as by portion 13a, with a support 6 which may be a terminal strip or a blade carrying a stationary or fixed contact 5. A co-operating movable contact 4 is mounted at the free end of a conventional snap action member 1 which may be of the bi-metal kind, but is preferably electromagnetically operated, and is arranged with its other end fixedly held at 2, to pivot about a V-groove at 3, as is known in the art. The rest position of the movable contact when not eni gaging the stationary contact is determined by a stop 10 and a spacer member 10a which preferably forms part of the stop 10. In the example shown the stop comprises a substantially cylindrical pin provided with at least one longitudinal slit SL. A sleeve 9 has a bore shaped and dimensioned to allow axial sliding movement of the pin in the sleeve during the assembly operation when force is exerted in the direction 11. Prior to this operation a feeler gauge 8 is inserted between the two contacts, and a means may be provided to exert a counter-force 12 sufficient to terminate the sliding movement of stop 10. When the force 11 is increased the member 10 is compressed longitudinally and, if suitably adapted, expands transversely to intensify or produce the frictional holding force between the surfaces of pin 10 and sleeve 9. At the end of the operation the force 11 is removed and the feeler gauge 8 is withdrawn. Thus the switching gap can be rapidly set to be accurately equal to the thickness of the feeler gauge 8, and can be safely fixed to retain a given value for a long time of service, using virtually a single operation, namely exerting pressure in the direction 11. Such an operation is also well suited for mass production with automatic machinery. As can be seen from the drawing the ends of the sleeve 9 can provide flanges 9a so that the sleeve forms a hollow rivet, and may hold a spacer 7 or other member between its upper flange and the top surface of the frame member 13.

Modifications are possible without departing from this invention. The snap action member may be of any conventional kind, and the movable contact may be held by a spring blade in any convenient manner known in the art without interfering with the essential features and effect of this invention. The outer surface of the stop and the bore surface in the support may be roughened to increase the friction.

What I claim is:

1. An electric switch having a stationary contact, a movable contact, a contact position limiting member, and a rigid frame, said contact position limiting member being longitudinally slidably adjustable in the direction of the contact gap dimension mounted coaxially of said two contacts by frictional engagement with said frame and projecting from said frame toward said contacts so as to limit the maximum gap between said contacts.

2. A switch as claimed in claim 1, wherein said frame includes a sleeve fixedly secured thereto, and said contact position limiting member is mounted on said frame by frictional engagement with the inner surface of said sleeve.

3. A switch as claimed in claim 1 wherein said con tact position limiting member forms a stop, and means for biasing said movable contact against said stop when not in engagement with said stationary contact.

4. A switch as claimedin claim 1, wherein the movable contact is of the snap action kind.

5. A switch as claimed in claim 1 wherein said frame is formed with a recess, and said contact position limiting member is frictionally mounted within said recess and formed so as to increase the pressure between its outer surface and the surface of: said recess when a compressive: force is exerted on said member longitudinally thereof and at right angles to said surfaces.

6. A switch as claimed in claim 5 wherein said con tact position limiting member has 'atleast one slit extending longitudinally therein whereby said member is expandably deformable under compression.

7. A switch asclaimed in claim 6, wherein the deformed surface of the member is non-resilient.

8. A method of setting to a desired close dimension the width of the interrupting gap between two relatively movable contacts the open position of at least one of which contacts is limited by a stop frictionally ad! justably supported coaxially with the contacts by a stationary member, comprising inserting a gauge of said desired dimension between the two contacts, applying a position adjusting and setting force to the stop in a direc- 4 tion coaxially thereof and of the two contacts so as to bring the two contacts to bear against opposite sides of the gauge by coaxially adjusting the frictionally supported position of the stop, then removing the gauge and leaving the stop held stationary by the friction of its support.

References Cited in the file of this patent UNITED STATES PATENTS 1,724,197 Hartzell Aug. 13, 1929 2,032,847 Kleinmann Mar. 3, 1936 2,428,172 Miller Sept. 30, 1947 2,505,225 Akroyd Apr. 25, 1950 2,521,887 Wihanto Sept. 12, 1950 2,671,151 Hollins Mar. 2, 1954 2,699,479 Gorham Jan. 11, 1955 2,729,715 Broch Jan. 3, 1956 2,747,167 Parrish May 22, 1956 2,898,418 Byam Aug. 4, 1959 FOREIGN PATENTS 241,794 Great Britain Oct. 29, 1925 

